Directional antenna control system



5 Sheets-Sheet 1 -Il- A. A. HEMPHILL ET AL DIRECTIONAL ANTENNA CONTROL SYSTEM June 24, 1958 A. A. HEMPHlLL ET AL DIRECTIONAL ANTENNA CONTROL SYSTEM June 24;, 1958 3 Sheets-Sheet 2 Filed March 22, 1955 U l' A I u I IT I I.I IVI I v Av III I II Y l l n I I I .I I I I II nl W N I' I .A .B .C 'D l .r l' I' l' I I u I. I I I ll I I I' I" I I I I I I v I l I u TI. I 1I IT I .Tl II.. I I' l' .l O O O O O O A B C D E .V

INVENTORS ALFRED A. HEMPHILL JOHN M. TEWKSBURY BY ATTF/VEYS June Z4, 1958 A. A. HEMPHILL ET AL DTRECTTONAL ANTENNA CONTROL SYSTEM 5 Sheets-Sheet 3 Filed March 22, 1955 INVENTORS ALFRED A. HEMPHILL BY JOHN M. TEWKSBURY ArroR/vsrs 2,840,814 Y Y DmECrIoNAL ANTENNA CONTROL VSYSTEM Alfred A. Hemphill, Baltimore, and .lohn Merle Tewksbury, Lutherville, Md., assignors to Bendix Aviation Corporation, Towson, Md., a corporation of Delaware Application March 22, 1955, Serial No. 495,942

Claims. (Cl. 343-121) This invention relates to a control system and more particularly to a type of control system adapted to, respond to the output of an antenna having a Vdirectional pattern including a null. Y

It is often desirable to cause such antennas to take up and maintain a directional orientation in which the null of the pattern is lined up with the source of a'received signal. In View of the fact that the amplitude of the received signal is at a minimum at the null, and the presence of noise interference which tends to mask the received signal and produce its own control effect, it is diflicult to generate a control signal -of sufficient magnitude to effect the desired orientation. Y

lt is an object of the present invention to provide a control system which will producev an effective control signal in the region of the null of a directional antenna pattern in spite of the presence of noise interference.

lt is a further object of the invention to provide such a system which will produce the desired result even though the desired signal exists in a noise field which is much greater in amplitude.

The above and other objects and advantages of the in-A vention are realized in a system in which the R. F. signal as picked up by a directional antenna is modulated in a f modulator at an audio frequency with a locally generated wave. The output of the balanced modulator is then combined with the output of a non-directional antenna.

The resulting wave is converted to I. F. and applied to A a synchronous detector Where it is compared to awaveform synchronized with the modulating frequency. All components except the modulating frequency are iiltered out, leaving a D. C. output having a magnitudeand sense which are functions of the magnitude and direction of the departure of the null from the vdirection of the received signal. This output is available as control voltage for the orientation of the directional antenna.

In the drawing: v Fig. 1 is a schematic circuit diagram of 'a system ern`- bodying the invention; Y l

Fig. 2 and 2a show a group of time related waveforms occurring at diiferent points in the system of Fig. l, when the controlled antenna is oriented with its null at one side of the directional line to the signal source; and, Fig. 3 and 3a show a similar group of waveforms as they exist when the null is on the sideof the directional line opposite to that of Figs. 2 and 2a.

Referring now more particularly to the drawing, the system illustrated in Fig. 1 includes a directional antenna 1, which is illustrated as a loop antenna, byway of example.

The output of the antenna 1 is applied to an R. F.

amplifier and 90 phase shifter 2. The phase shifter is Y The amplified and phase shifted signalV is applied in parallel to a balanced modulator 3, to which is also apan I. F. signal whichv is amplified in amplifier 13 andV 2,340,814 Y Patented June 24,1958

ice d 2 plied in push-pull a 48 cycle sine wave from an oscillator 4.

:The output of the balanced modulator is applied to a primary winding 6 of a transformer 5. Toa second pri-r mary winding 7 is applied the received output of a nondirectional sense antenna 8. The tuned secondary 9 of'this transformer applies the combined outputs of the.' balanced modulator and sense antenna to an R. F. amplilier 1t). The output of this amplifier is mixed with'that of an R. F. oscillator 11 in a first detector 12.to produce applied to the tuned primary of a transformer 14.`

vThe output of the audio oscillator 4 is also applied by way Yof the tuned secondary of Vtransformer 14 to the synchronous detector, being applied by way of a conductor 15 to one of the junction points between the coil 16 and capacitor 17 making up the secondary of the transformer. The remainingjunction of these components is connected to the anode of a diode 13 and the cathode of a Ydiode 19 making up a `synchronous detector 20.

The cathode of diode18 and the anode of diode 19 are joined by way'of a pair of serially connected,V equal valued resistors 21 and V22. The cathode of diode 18 and the anode of diode 19 are connected to ground byway of re- Y spective capacitors 23 and 24 which have equalvalues.

The time constants of the resistance-capacitance combinations 21, 23 and 22,24 are such that the I. F. is affordedV Y an easy path to ground while the A. F. is not attenuated.' The junction point of resistors 21 and V22 is connected by` way of a resistor 2S to aiD. C; amplifier andcontrol unit 26 which provides control voltage for aloop driveV motor 27. This motor drives the Vloopl. The junction of re# sistor 25 and amplifier 26 is connected to ground through.

a capacitor 28. The time constant of theV combination 25, 28 should be such as to integrate the output at the junction of 21 and 22 over a desired interval of time.M

, Audio output is taken in push-pull from thecathode of diode 18 and the anode of diode 19 by way of conductors 31 and 32 which are connected, by way of iilter networks composed of capacitors 33, 34 and resistors 35, 36 to the."

respective grids of two triodes 37, 38 which feed .a speaker 39 through a transformer 40.

In describing the operation of the system of' Fig." l,

reference will be had to the waveforms depictedin Figs. K

2, 2a, 3 and 3a, those shown in Figs. 2 and 2a being those existing in the system when the null of the loop sensitivity pattern isdirected to one side of the direction'of'signal reception and those of Figs. 3 and 3a being the corre` sponding waveformsexisting when the` null is on the other side of Vthat direction.

The waveform A is the R. F. output of the loop when v receiving an unmodulated wave. The waveform A is identical therewithl except thaty the two waveforms are phase opposition.

The waveforms B and D are the two phase opposed of the balanced modulator conducts,.the other halfbeing Y cut olf. The waveforms C and E' have envelopes identical with the corresponding waveforms C and E, but Athe radio frequency content is in phase opposition to that of the corresponding waveform of Fig. 2.

The waveformsfF and F are identical and represent the output of the non-directional antenna 8 which is cornbined with Vwaveforms C and D or C and DV in the transformer 5. The resultant of this action is the wave form G or G. The first half `cycle ofthe Yenvelope of G is of large amplitude, whereas the second half cycle is of small amplitude. This results from the phase of the two outputs C and E. That of C is in phase with the waveform F and thus adds to its amplitude, whi le the waveform E is out ot phase with it and thus diminishes its amplitude.

The waveform G resulting from the combination of waveforms C', E' and F' has an envelope vwhich is in phase opposition to that of waveform G due tothe p'hase opposed relationship between waveforms C and C', and E and E'.

The waveform G or G' is that applied to the R. iF.l

amplifier l@ and the first detector 12. where it is converted to i. F., but the envelope remains unchanged. in the secondary of the transformer 14 the resulting wave is combined with H or H', which are identical with waveforms B and B except that the amplitude is indicated as much greater. While the amplitude of waveforms B and D are illustrated as much less than that of H, they may actually have the same value without producing from the balanced'modulator an output of any greater relative amplitude than that illustrated.

The waveforms H or H', being applied to the synchronous detector, will during its positive half cycles render the diode 1S conductive and the diode 19 non-conductive. During its negative half cycles it will render diode 19 conductive and diode 18 non-conductive.

The curve I indicates the waveform appearing at the point 29 of the synchronous detector when the null is to one side of the direction of the signal source and the curve I' indicates the voltage at the same point when the null is to the other side of that direction. The maximum ordinate ot the curve l is larger than that of curve I', since the maximum ordinate of the positive lobe of curve H coincides with the maximum ordinate of curve G, whereas the maximum ordinate of the positive lobe of curve H' coincides with the minimum ordinate of curve G'. Y

The curves J and I give the same information with respect to the point 30 of the synchronous detector as the curvesl and I did with respect to the point 29. In this case the maximum ordinate of curve I exceeds that of curve I, reliecting the coincidence of the maximum ordinate of curve G with the maximum ordinate of the negative lobe of curve H'.

Curves K and K indicate the 'waveform appearing at the junction of resistors 2l and 22. While this waveform has a generally sine wave shape, the lobes are of unequal amplitude. In the curve K the positive lobe is larger, while in the curve'K'the negative lobe is larger. The integrating action ofresistor and capacitor 28 will derive/from the waveform H a positive D. C. voltage, while from the curve H' a negative D. C. voltage will result. j

The portions of the system of Fig. l which are shown as boxes, are of conventional maire up and no detailed disclosure thereof is deemed necessary.

The audio circuit is likewise conventional. 'A Any modulation carried by thc I. F. is applied in alternation to the tubes 37, 38 from the points 29 and 3i?. Since in each cycle of the forty-eight cycle reference voltage the positive lobe is applied from point 29 andthe'negative lobe from point 39, the wave is substantially eliminated from the audio output.

Use of the invention is capable of providing perfect motor control under conditions in which the amplitude of interference greatly exceeds that of the desired signal. In la system built and tested in which the desired signal appeared as two percent modulation of the carrier and, interference signals caused one hundred percent modula-v tion of the carrier at the same time, motor control without any apparent eiect from the interferenceA was achieved. This result is possible because the control signal is due to the continuance of one or the other of two definite phase relationships between the two fortyeight cycle inputs to the synchronous detector. Any

interfering signal would be applied to the detector only pattern including a null, said system driving said antenna until said null coincides with the direction of origin of a received signal, said system comprising: means amplifying and shifting the Vphase' ol said received signal by 90, a balanced modulator, means applying said amplii lied and phase shifted signal to said balanced modulator,

an audio oscillator, means applying the output of said audio oscillator to said balanced modulator in phase opposition, a non-directional antenna., means combining the output of said non-directional antenna with the output of said balanced modulator, thereby providing a resultant waveform` having the frequency of Said'received signal and modulated with the output of said audio oscillator, the phase of said modulation beingin one sense when the said null is on one side of the direction of origin of said signal and'in the opposite sense when the said null is on the other :side of said direction, means converting the signal frequency of saidA resultant waveform to an intermediate frequency, a synchronous detector, means applying said converted signal to said synchronous detector, means simultaneously applying the output of said audio oscillator to said synchronous detector, said synchronous detector comprising a pair of diodes, means connecting the cathode of one of said. diodes to the anode of the other and having said converted signal and said audio oscillator Voutput applied thereto, means including a capacitor connecting each of the remaining electrodes of said diodes to ground, means connecting said remaining electrodes to each other, the last named means -comprising a pair of serially joined resistors, said resistors and capacitors having values such as to attenuate intermediate frequencies appearing at said remaining electrodes, but such as not to attenuate audio frequencies, an output connection to the junction of said resistors and an integrating network operable upon voltage appearing at said output connection, voltage responsive means driving said directional antenna in orientation and means applying the voltage present at said output connection to said driving means to control the operation thereof.

2. A systemy for controlling the orientation of an antenna having a directional pattern including a null, said system comprising: means responsive to the reception of a signal by said directional antenna to generate a voltage Waveform comprising a carrier wave modulated at an audio frequency, said modulation having one phase when said null is positioned on one side of the direction of origin of a received signal and having an opposing phase when said null is positio-ned on the other side of said direction, a synchronous detector comprising a pair of diodes having the anode of one conductively connected to the cathode of the other, a pair of resistors serially connected between the remaining electrodes of said diodes, a respective capacitor connectingeach of said remaining electrodes to ground, said resistors and capacitors having values such that intermediate frequencies appearing at said remaining electrodes are attenuated but audio frequencies are not, means applying said voltage waveform to said connected electrodes, means applying to said connected electrodes an alternating voltage synchronized with said audio frequency and having the same phase as said modulation has when said null is positioned on said one side of said direction, means integrating the voltage appearing at the junction of said serially connected resistors, voltage controlled motor means driving said antenna `Aand means applying said integrated voltage as control voltage to Vsaid motor means.

3. A..Sfynchr,0'nous detector comprising a pair of diodes,

means applying to the anode of one of said diodes and the cathode of the other a signal comprising a carrier modulated by a wave of lower frequency, means applying to said anode and cathode in parallel, simultaneously with the application of said signal, a wave having the frequency of said modulating wave, means including resistance means conductively `connecting the remaining electrodes of said diodes, a respective capacitor connecting each of said remaining electrodes to ground, said resistance means and capacitors having values such that intermediate frequencies appearing at said remaining electrodes are attenuated but audio frequencies are not, an output connection to an intermediate point of said resistive means, and an integrating means coupled to said intermediate point and operable to integrate the voltage appearing at said output connection, whereby a D. C. voltage output having a sense and magnitude which are functions of the phase relationship of said modulating wave and the last named wave is derived by said detector.

4. In combination with a source of carrier frequency voltage modulated by a wave of lower frequency having one of two possible phase opposed states, a parir of rectifiers having their unlike terminals joined to form a series circuit, means applying said modulated voltage to the junction of one of said pairs of unlike terminals, means simultaneously applying to said junction a wave of the same frequency as said modulating wave and having one of said two phase opposed states, the last named wave having such an amplitude as to render said rectifiers alternately non-conducting for a major portion of a half cycle thereof, the means joining the remaining unlike terminals 5. A system for driving an antenna having a direcvtional pattern including a null, said system driving said of said rectifiers comprising a balanced impedance netantenna until said null coincides with the direction of i origin of a received signal, said system comprising: means amplifying and shifting the phase of said received signal by a balanced modulator, means applying said ampliied and phase shifted signal to said balanced modulator, an audio oscillator, means applying the output of said audio oscillator to said balanced modulator in phase opposition, a non-directional antenna, means combining the output of said non-directional antenna with the output of said balanced modulator, thereby providing a re-` sultant Waveform having the frequency of said received signal and modulated with the output of said audio oscillator, the phase of said modulation being in one sense when the said null is on one side of thedirection of origin of said signal and in the opposite sense when the said null is on the other side of said direction, means converting the signal frequency of said resultant waveform to an intermediate frequency, a synchronous detector, means applying said converted signal to said synchronous detector, means simultaneously applying the output of said audio oscillator to said synchronous detector, means selectively attenuating intermediate frequencies from the output of said synchronous detector, means integrating the output of said synchronous detector, voltage' responsive means driving said directional antenna in orientation and means applying the outputk of said integrating means to said driving means to contro the operation thereof. y

References Cited in the file of this patent UNITED STATES PATENTS Selove Jan. 18,Y 1955 

